Override-nullifying scheme for train control system



United States Patent 1 3,539,226

[ 72] Inventor Wayne ll. Barber [56] References Cited walel'lown, New York UNITED STATES PATENTS NO. zzlz lzl low 3,240,536 3/1966 Rouillon 303/16 3,374,035 1 6 d 4s Patented Nov. 10,1970 9 8 303/20 [73] Assignee General Signal Corporation P Exammer Duane Rage! a corporation of New York 8 and Osman" ABSTRACT: A train control system in which a slave locomotive is controlled by command signals transmitted from a [54] SCHEME FOR TRAIN remote master locomotive. A selectively operable override 5 cl i 2 D in Fl control maintains previously commanded propulsion and 3 raw 8 braking conditions at the slave locomotive in the event of a [52] US. Cl 303/20, discontinuity in signal transmission, and an override-nullifying 303/16 control automatically causes the slave locomotive to idle and [51] Int. Cl. B60t 13/68 prevents its brake valve from admitting air into the trainlined [50] Field of Search 303/3, 16, brake pipe when the rate of change of flow into the brake pipe 17, 20, 28, 40, 42, 44, 47, 60, 77, 86 'at the slave unit exceeds a predetermined value.

MAST SLAVE f /LOCOFA%TIVE I02 Y /LOCOMOTIVE 103i I05 [Q4 00 00 v 0 JO ou POWER SUPPLY I04 I L i280.

N I e 128 |22 l s VOLUME 0 V 5 3o JWYQE I24 1 5 RESERVOIR I5 I P Q I16 n2 n5 K 129 M in I3! I34 EQUALIZING I13 I07 RESERVOIR H9 '08 MAIN RBERVOIR 109 OVERRIDE-NULLIFYING SCHEME FOR TRAIN CONTROL SYSTEM BACKGROUND AND SUMMARY OF THE INVENTION The countrys railroads are currently using a train control system in which a portion of the locomotive consist is positioned back in the train and is operated as a slave unit by command signals transmitted over a radio link from the lead locomotive or master unit. The system is known by the name LOCOTROL. When this system is in use and the communication link is complete and command and report back signals are received by the two units at a regular rate, the propulsion and braking conditions of the slave unit are maintained in synehronism with the corresponding conditions of the master unit. But, when there is a break in signal continuity, the system automatically precludes the brake valve on the slave from supplying air to the trainlined brake pipe, and thus counteracting a brake application initiated at the lead locomotive, and in itiates a programmed reduction in the propulsion effort of the slave locomotive. In situations where a temporary signal be energized before the train enters the suspect region and which serves to maintain previously commanded propulsion and braking conditions at the slave during a subsequent period of signal discontinuity.

In certain circumstances, it is necessary to increase braking effort or even stop the train during override operation. In order to provide this capability, the LOCOTROL system incorporates an overridenullitication control which causes the slave locomotive to idle and prevents its brake valve from feeding air into the brake pipe. This control is operated automatically by a device which responds to the rate at which air is admitted into the brake pipe at the slave unit. If, during an override period, the engineer commences to exhaust air from the brake pipe at the master unit in order to effect a brake application, the brake valve on the slave unit will attempt to counteract this change by supplying air to that pipe, and the nullification control will automatically be effective to idle the slave and interrupt the feeding action of its brake valve. As a result, the reduction in brake pipe pressure will be propagated through all the cars, and the train will be retarded as though the slave unit were not present.

The flow sensor used in the override-nullification control is set high enough that normally it is not triggered by the flow accompanying the allowable A.A.R. brake pipe leakage rate of 5 psi. per minute. However, if the leakage rates on the cars ad jacent the slave are unusually high, or if there is excessive leakage in the train, premature operation of the nullification control can take place. Moreover, if override action is initiated in the period following release ofa service brake application when the rate of flow of air into the brake pipe is still relatively high, the sensor immediately will render the nullification control effective and preclude proper operation of the system. And these problems cannot be cured merely by raising the setting of the flow rate sensor because that measure could preclude cnergization of the nullification control in cases where the override control is maintaining a partial service braking application The object of the present invention is to provide an improved override-nullifying scheme which eliminates the problems just mentioned. In accordance with the invention, the nullification control is operated by a device which senses the rate ofchange of flow into the brake pipe, rather than the rate of flow itself. Inasmuch as any brake pipe reduction initiated from the head end of the train will cause the brake valve on the slave unit to increase markedly the rate of flow into the brake pipe, incorporation of the new sensor enables the nullification control to suppress override action as required. And, since the new sensor is insensitive to the absolute value of flow rate, the new scheme is ableto perform this function regardless of whether brake pipe flow rate is high or low, As a result, premature operation attributable to leakage or brake pipe charging is avoided, and suppression of the override control is guaranteed even in situations where the override is maintaining a partial service brake application at the instant the nullification control is activated.

BRIEF DESCRIPTION OF THE DRAWING The preferred embodiment of the invention is described herein with reference to the accompanying drawing in which: 7 FIG. 1 is a schematic diagram of a train employing the LOCOTROL system.

FIG. 2 is a schematic diagram showing the improved nullification scheme and those portions of the LOCOTROL system needed to explain its operation.

DESCRIPTION OFTHE PREFERRED EMBODIMENT As shown in FIG. I, the locomotive consist for a train employing the LOCOTROL system is made up of a lead or master unit 101,.tnd a slave unit I02 which is positioned back in the train. Each ofthe locomotive units carries a control unit 103 or 104 including mechanism for controlling-propulsion effort and dynamic braking, equipment for controlling the pressure in a trainlined brake pipe 105, and a radio transmitter and receiver. Normally, the propulsion and braking conditions at slave locomotive 102 are controlled by command signals transmitted from master locomotive IOI'and the corresponding conditions at the two units are kept in synchronism. Thus, during brake operations, air is withdrawn from or supplied to brake pipe 105 at each station.

Referring to PK). 2, the controlunit 104 on slave locomotive 102 includes a conventional Type 26-C brake valve 106, whose pertinent'ports are designated by their usual identifying numerals I, 5, I5, 30 and 53, a main reservoir 107 which delivers air under pressure to valve 106 through supply pipe 108 and the No. 30 port, and an equalizing reservoir 109. Brake valve 106 contains all ofits normal components and can be operated in the usual way to control brake pipe pressure when the remote control system is turned off. However, during operation of the LOCOTROL system, the handle of valve 106 is kept in release position and most of its functions are performed by separate solenoid valves operated by the system's controller 111. Four of these valves deserve mention here. The first two solenoidvalves, labeled I12 and 113, are used to control the pressure in equalizing'reservoir 109 during service applications and releases; the valve 112 being interposed in an atmospheric vent connection 114 and serving to reducereservoir pressure, and the valve 113 being interposed in a supply connection 115 leading from the No. 15 port'of brake valve 106 and serving'to charge the reservoir. Since the setting of the regulating portion of brake valve 106 is not changed during system operation, it will be understood that the pressure at the No. 15 port is maintaincdconstant at the level of the selected maximum brake pipe pressure. The other two solenoid valves, namely valves I16 and 117, are interposed in vent and supply connections I18 and 119, respectively, leading to the No. 53 port, and thus serve to control operation'of the brake pipe cutoff valve in brake valve 106: When valve 116 is open and valve 117 is closed, the cutoff valve allows communication between the relay portion of brake valve 106 and the No. 1 port, so the relay is able to establish and maintain a pressure in brake pipe I05 equal to the pressure in equalizing reservoir 109. On the other hand, when valve 117 is open and valve 116 is closed, the brake pipe cutoff valve is held shut by the pressurized air delivered to the No. 53 port, and the relay portion of valve 106 is precluded from admitting air into brake pipe 105.

The circuits of controller 111, which, it will be understood, controls the propulsion and dynamic braking efforts of slave locomotive 102 as well as the valves I12, I13, I16 and 117, normally respond to and are conditioned by the command signals received from master locomotive 101 or by the interruption ofthose signals fora preseribed period of time. If the radio communication link between the master and slave is intact, controller 111 maintains the propulsion and braking conditions at the slave in synchronism with the corresponding conditions at the master. Thus, when the brakes are released and the brake pipe pressure control equipment in control unit 103 is maintaining the pressure in brake pipe 105 at the selected maximum value, controller 111 will keep valves 112 and 117 closed and keep valves 113 and 116 open. This insures that the pressure in equalizing reservoir 109 will be maintained at the setting of the regulating portion of brake valve 106, and that the brake pipe cutoff valve will allow com munication between the relay portion of valve 106 and brake pipe 105. As a result, brake valve 106 will supply air from reservoir 107 to brake pipe 105 as needed to compensate for leakage, and thereby aid the brake valve on master unit 101 in its function ofmaintaining the brake pipe fully charged.

When a service braking application is initiated, the braking equipment on master unit 101 will commence to reduce brake pipe pressure to the selected level, and simultaneously controller 111 on slave 102 will close valve 113 and hold valve 112 open for a period of time corresponding to the selected reduction in brake pipe pressure. The resulting decrease in equalizing reservoir pressure causes the relay portion of brake valve 106 to bleed air from brake pipe 105 and again establish and maintain equality between the brake pipe and equalizing reservoir pressures. The action of brake valve 106 supplements the brake pipc-venting action of the brake valve on master unit 101 and thereby hastens the propagation of the pressure reduction through the train. When the brakes are subsequently released, controller 111 will open valve 113, thereby allowing equalizing reservoir 109 to be recharged to the setting of the regulator portion of valve 106 and causing the relay valve in valve 106 to recharge the brake pipe 105 to a corresponding level.

lf there is an interruption in the radio communications between slave 102 and master 101 which persists for a prescribed length of time, controller 111 will automatically effeet a progressive reduction in the propulsion effort of the slave locomotive 102 and close and open valves 116 and 117, respectively. When valve 117 opens, the No. 53 port of valve 106 is pressurized and the brake pipe cutoff valve is closed. This, of course, precludes brake valve 106 from supplying additional air to brake pipe 105. If, on the other hand, the discontinuity in signal transmission was anticipated and the override control had been energized, controller 111 would maintain the previously commanded propulsion and braking conditions during the period in which the communication link was interrupted. In this case, valves 116 and 117 would be kept open and closed, respectively, and brake valve 106 would not be precluded from maintaining brake pipe pressure at the commanded level.

1n the illustrated embodiment, the action of the override control is nullified by momentary opening ofa switch 121 interposed in a supply path to certain ofthe circuits in controller 111. During normal operation, actuation of the switch 121 has no effect upon the controller. However, if the switch is opened, even momentarily, during an override period, controller 111 automatically causes the power plant of slave locomotive 102 to idle, and also operates valves 116 and 117 so as to pressurize the No. 53 port of valve 106 and thereby effect closure of the brake pipe cutoff valve. The nullification scheme 122 provided by the invention serves to automatically open switch 121 and produce the desired override-nullification action when the rate of change of the flow rate into brake pipe 105 through valve 106 exceeds a predetermined value.

As shown in FIG. 2, the nullification scheme 122 comprises a volume reservoir 123 which is connected with supply pipe 108 through a branch pipe 124 containing a flow restrictor or choke 125. a second choke 126 interposed in pipe 108 between the junction 127 with branch pipe 124 and main reservoir 107, and a fluid pressure motor 128. Motor 128 includes a biasing spring 128a and is arranged to open switch 121 upon the occurrence of a predetermined difference between the pressures at volume reservoir 123 and junction 127. Preferably, each of the chokes 125 and 126 is provided with a bypass path 129 or 130 containing a check valve 131 or 132 oriented as shown. The bypass 129 around Choke 125 in sures that the pressure atjunction 127 will not exceed by a signiticant amount the pressure in reservoir 123, and thus precludes motor 128 from exerting a damaging closing force on switch 121. Bypass path 130, on the other hand, permits rapid charging of brake pipe 105 following an emergency application or any other occurrence which results in complete venting of the brake pipe.

During operation, volume reservoir 123 will be charged through pipes 108 and 124. If the flow demand imposed on main reservoir 107 is constant or changes slowly, the chokes 125 and 126 will have no delaying effect, and the pressures at volume reservoir 123 and at junction 127 will remain equal. Therefore, regardless of the magnitude of the flow rate, spring 128a will keep nullification switch 121 closed. This, ofcourse, means that neither excessive leakage on cars adjacent to unit 102 nor initiation of override control while brake valve 106 is charging pipe 105 will result in override-nnllitication action. On the other hand, it during an override period the operator commences to exhaust air from brake pipe 105 at master locomotive 101 in an effort to apply the brakes, the relay portion of brake valve 106 will initially increase the rate of flow into brake pipe 105 and attempt to counteract the desired pressure reduction. The magnitude and suddenness of this change in flow rate are such that chokes 125 and 126 will cause the pressure at junction 127 to decrease momentarily relatively to the pressure at volume reservoir 123. This pressure differential is sufficient to enable motor 128 to open switch 121 and thereby institute override-nullification action. One result of this is that controller 111 will close and open valves 116 and 117, respectively, to effect closure of the brake pipe cutoff valve and preclude brake valve 106 from impeding propagation of the brake pipe reduction through the train. Although the pressure differential just mentioned does not persist, this is of no consequence because momentary opening of switch 121 is all that is required to cause controller 111 to perform the nulliflcation function.

In cases where the nullification scheme 122 is set to respond to a relatively small rate of change of flow, it sometimes hap-' pens that the normal variation in main reservoir pressure attributable to the characteristics ofthe unloader used on the air compressor can cause inadvertent opening ofswitch 121. This problem is eliminated in the illustrated system by including means for regulating the pressure in pipe 108 upstream of choke 126. As shown in FIG. 2, the regulating means comprises a conventional Type J-l relay valve 133 which is interposed in the connection between pipe 108 and reservoir 107 and is piloted by the output pressure of a conventional Type N-l reducing valve 134 which is supplied by the reservoir. Reducing valve 134 is set to produce an output pressure slightly below the lower limit of the compressor operating range; therefore, relay valve 133 automatically delivers air to pipe 108 at an equal, and consequently uniform, pressure.

Iclaim:

1. In a train control system of the type in which a slave locomotive is controlled by command signals transmitted from a master locomotive and which includes brake valve mechanism on each locomotive for controlling the pressure in a trainlined brake pipe, a selectively operable override control for maintaining at the slave locomotive previously commanded propulsion and braking conditions in the event of a discontinuity in signal transmission, and override-nullitication means for causing the slave locomotive to idle and for preventing its brake valve mechanism from admitting air into the brake pipe, the improvement which comprises means 122 for automatically operating the override-nullification means when the rate ofchange of flow to the brake pipe through the brake valve mechanism 106 on the slave locomotive 102 exceeds a predetermined value.

z. The improved system defined in claim 1 in which the brake valve mechanism on the slave locomotive has a supply pipe through which it receives air' under pressure from a main reservoir; and the means 122 for operating the override-nullification means comprises a. a first flow restrictor I26 interposed in the supply pipe 108; b. a branch pipe 124 connected with the supply pipe 108 at the brake valve mechanism side of the first flow restrictor and leading to a volume reservoir 123; c. a second flow restrictor 125 in the branch pipe 124; and (1. means 128 responsive to the pressures at opposite sides of the second flow restrictor foroperating the override-nullification means when the pressure at the volume reservoir side of the restrictor exceeds the pressure at the opposite side by a predetermined amount. 3. The improved system defined in claim 2 in which the branch pipe 124 has a restrictor bypass path 129 containing a check valve l3 l oriented to permit flow toward, but not away from, the volume reservoir 123.

4. The improved system defined in claim 2 in which the means 122 for operating the override-nullification means also includes a pressure regulator I33. [34 for maintaining constant the pressure in the supply pipe 108 at the main reservoir side of the first flow restrictor I26.

5. The improved system as defined in claim 2 in which:

a. the branch pipe 124 has a restrictor bypass path I29 containing a check valve l3l oriented to permit flow toward, but not away from, the volume reservoir 123;

b. the supply pipe 108 has a restrictor bypass path containing a check valve 132 oriented to permit flow from, but not toward, the main reservoir 107; and

c. the pressure in the supply pipe 108 at the main reservoir side of the flow restrictor 126 is maintained constant by a pressure regulator [33, 134. 

